Colonization of the Krakatau islands by vertebrates

80 species of non-marine, non-migrant vertebrates, excluding also shore birds, have been recorded from the Krakatau archipelago since the explosive eruption of 1883.73 of these are believed to have established breeding populations and successfully colonized the islands (47 resident land birds species, 13 bats, 11 reptiles and 2 rats). A large proportion of these colonizers consists of species with wide distributions, broad ecological tolerances and/or association with urban or rural situations. 11 of the 73 colonizing species (8 resident land birds, 2 reptiles and a bat) have become extinct on the islands. No amphibian species has yet been recorded and successful non-volant mammal colonists consist only of rats.Species turnover is considered to be largely associated with successional change of habitat. Progressive loss of coastal habitat through marine erosion and of open inland habitats through forest formation and canopy closure has been important and volcanic activity is indicated in the case of one or two extinctions.Active flight has been the predominant dispersal method (63 of the recored species, 79%, are birds or bats). Of the 17 recorded non-volant vertebrates, 6 species are assessed as having dispersed by swimming, 4 by means of natural rafts and 7 most likely through human agency (on boats). Human-assisted dispersal is seen to be of increasing importance with the increasing number of tourist visits and this may prove to be significant in determining the nature and rate of future colonization by vertebrates.     

Colonisation of the Krakatau islands by invertebrates

Arrival of invertebrates on the Krakatau islands, and the development of invertebrate assemblages there since 1883, are reviewed. Many data are imprecise, and difficulties of interpretation are outlined. A few well-known groups, such as butterflies, are used to suggest that much colonisation so far has been by relatively generalist species,and that the rate of addition of new species may become slower as the less vagile specialists characteristic of later successional vegetation may find natural colonisation harder. Studies of the assemblages developing in association with particular plant species are likely to be helpful in assessing future trends of invertebrate colonisation.     

台湾大地构造环境与地震

台湾、吕宋和琉球等岛弧区是中新世以来地震多发区.1999年9月21日台湾南投大地震以其震级大、震期长和损失惨重引起国内外关注.本文以台湾所处大地构造环境特征探讨发震机制和9.21大地震对地学界的警示.     

The copper deposits and geotectonic setting of the Thethyan Eurasian Metallogenic Belt

The paper is concerned with the relationships between porphyry copper and massive-sulfide copper deposits, and their geotectonic environments in the Tethyan Eurasian Metallogenic Belt. This belt is located between the Afro-Arabian and Eurasian plates, almost 10,000 km long, linking the Alpine metallogenic system in Europe with Pacific system. A plate tectonic model for the tectonic evolution of this metallogenic belt in space and time is presented with emphasis on specific features of individual sectors.The paper was presented on the 25th International Geological Congress in Sydney, August 1976 (Symp. 104. 1)     

阿尔金高压变质岩带的特征及其构造意义

阿尔金构造带存在两条高压变质岩带,一条为高压变泥质岩带,出露在阿尔金中段北部红柳沟-拉配泉东西向蛇绿混杂岩带之中的贝克滩东侧,东西向展布约几公里;另一条为榴辉岩带,出露在阿尔金南缘的江格萨依南-米兰河上游一带的北东向隆起带上,断续延伸约200km.区域构造背景、高压变质岩石的变质历史及顺时针型P-T轨迹和年代学研究表明,这些高压变质岩石的形成应与板块俯冲、碰撞活动有关,它们分别代表了显生宙初塔里木板块东南缘的两次俯冲-碰撞活动.这一成果为阐明阿尔金左行走滑断裂系的早期演化及板块增生提供了重要依据.     

Genetic types of gold deposits and their setting in geotectonic structures

Acritarch assemblages at the Cambrian-Precambrian boundary correlate the Siberian Tommotian deposits with the East European Lontova horizon, and the Nemakit-Daldyn horizon with Vendian deposits in Malyy Karatau.     

东北东部地球物理及地质块体特征——对大地构造环境演化的追溯

通过区域地球物理场多重信息的综合研究 ,可将东北东部地球物理及地质块体划分为A、B、C三类。它们在空间上有序的分布 ,特征上各自相异。揭示出所共处的区域岩石圈的大地构造环境演化历史的全过程。B类地块代表了太古宙陆块的形成 ;C类地块反映了古亚洲构造域复杂的造山过程 ;A类地块则揭示出中生代以来壳幔作用动态过程—拆层作用和盆山构造的形成及对前期构造的强烈改造     

东北东部地球物理及地质块体特征——对大地构造环境演化的追溯

通过区域地球物理场多重信息的综合研究，可将东北东部地球物理及地质块体划分为A、B、C三类，它们在空间上有序的分布，特征上各自相异，揭示出所共处的区域岩石圈的大地构造环境深化历史的全过程，B类地块代表了太古宙陆块的形成；C类地块反映了古亚洲构造复杂的造山过程；A类地块则揭示出中生代以来壳幔作用动态过程－拆层作用和盆山构造的形成及对前期构造的强烈改造。     

冀西北高压麻粒岩带构造环境的再思考

在崇礼岛弧型绿岩带与怀安古陆块之间,从怀安大虎沟,经宣化大东沟至赤城沤麻坑发育一条大体呈东西走向并向南倾斜的板状高压麻粒岩带。其中轻稀土亏损的洋中脊型拉斑玄武岩（ＴＨ１） 的存在显示部分洋壳残片的可能卷入。变质条件（８５０ ～９００ ℃,１３ ～１４ＧＰａ） 表明它属于俯冲杂岩。同时比怀安陆块（２ ９００ Ｍａ） 显著年轻的模式年龄（２ ７００ ～２ ６００ Ｍａ） 证明了它的增生性质。从综合地球化学、变质作用和年代学资料来看,它们不属于连续下地壳剖面的最下部,而更可能是新太古代侧向增生的弧后混杂岩带。     

Low-grade metamorphism and geotectonic setting of the Macuchi Formation, Western Cordillera of Ecuador

Abstract The Cretaceous-Eocene basic to intermediate marine volcanic rocks of the Mucuchi Formation constitute the Western Cordillera in northern Ecuador. Their chemical features mostly correspond to those of tholeiitic basalts with some calc-alkaline affinities and suggest an oceanic island arc setting. The Macuchi rocks are affected by low-grade, non-deformative metamorphism, characterized by zeolite, prehnite-pumpellyite and lower greenschist facies assemblages. Depth-zonation is suggested by the downward mineral sequence: (i) laumontite+ (pistacitic epidote, pumpellyite + prehnite); (ii) pumpellyite+ prehnite + pistacitic epidote; (iii) actinolite+biotite+ pistacitic epidote + chlorite. This broad zonation and the chemistry of individual minerals point to an interaction between the volcanic rocks and sea-water under a moderate to high thermal gradient (= 75° C/km?). Alteration appears to have been dependent primarily on fluid control (volume, pressure, composition), temperature and reaction kinetics which together partly overshadow the role of load-pressure. Compositional variations of a mineral species at the scale of a contiguous flow or even at the scale of a thin section show that intensity of alteration was spatially uneven depending on rock permeability and consequently, metastable equilibrium commonly exists. However, a progressive approximation to equilibrium as a result of P–T control is shown by the mineralogy. A high f_o2 of the fluid phase is evident from the mineral chemistry. The metamorphism of the Macuchi volcanics is similar to the hydrothermal-burial type produced during the development of a volcanic arc where lavas and volcanoclastics accumulated in a shallow marine environment. However, some of its characteristics point to a transition toward systems defined by a higher T/P ratio such as those found in ocean-floor metamorphism. A model is proposed in which the Macuchi volcanics are assigned to an oceanic island arc generated contemporaneously with a marginal basin which has opened as the outcome of progressive north-south attenuation of the continental crust due to mantle diapirism.     

The birds of Anak Krakatau: the assembly of an avian community

The avian colonization of Anak Krakatau, an emergent volcanic island, is described for the period 1952–1991 with emphasis on the resident land birds. The few species that had colonized the island by 1952 were destroyed in a volcanic eruption. Recolonization has been rapid and extensive but only documented by regular surveys that began in the 1980s. The waves of avian colonists associated with the following stages of plant succession are described: pre-vegetation, beach and grassland pioneers, casuarina woodland and mixed forest. Rainforest frugivores first reached the island in 1985 coinciding with the fruiting of the first fig trees. The three stages of plant succession and the bird communities associated with them co-exit on three separate lowland sites with about a 10–15 year delay between them. The guilds of shorebirds, predators, nectarivores, frugivores and insectivores are described. Densities of insectivores are very high; however between 1986 and 1990, some generalist species have fallen in abundance whereas some specialists have increased. The establishment species have fallen in abundance whereas some specialists have increased. The establishment of new colonists, especially pigeons, has been limited by the arrival of two species of falcons.     

S- and I-type granitoids of North Victoria Land,Antarctica, and their inferred geotectonic setting

In the context of Gondwana North Victoria Land forms the Antarctic conjugate terrain to the East Australian Lachlan Fold Belt, where the distinction between S- and I-type granitoids was first worked out (Chappell &White 1974). Thus the area was considered a good testing ground for the hypothesis when the German Antarctic North Victoria Land Expedition (Ganovex) resumed fieldwork there in 1979/80.It was known at that time that there existed a Cambro/Ordovician and a Devonian/Carboniferous granitoid generation, which, in analogy to Australia, were taken to be related to two different orogenetic events. Our geological, petrographical and geochemical investigations, together with radiometric age dating, revealed that this is true only for the older granite generation. The younger generation is in fact anorogenic. At the same time, it became obvious that the S- and I-type classification did not completely fit the observed field data. At this pointPitcher's (1982) subdivision of the I-types into a »Cordilleran« and a »Caledonian« suite offered a solution to account for the observed irregularities.At about the same time, plate tectonic models based on evidence independent from the granite classification were developed for this part of the active Gondwana margin. This offers the opportunity to crosscheck the tectonic environment derived from the granite classification:The characteristics of the older, Cambro/Ordovician granitoids allow a perfect accommodation in the model of an active margin above a subduction zone as derived from other evidence.For the younger (Devonian/Carboniferous) granitoids, however, the postulated tectonic setting (post-collisional uplift and faulting) could not be verified in North Victoria Land.It is concluded thatPitchers classification is applicable in its petrographic and geochemical aspects but that the tectonic environment postulated for the production of »Caledonian« I-type granitoids may not be the same in all investigated areas.

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Zusammenfassung Im Gondwana Rahmen bildet Nord Victoria Land das antarktische Pendant zur ostaustralischen Lachlan Mobilzone, wo die Einteilung von Graniten in S- und I-Typen entwickelt wurde (Chappell &White 1974). Deshalb war eine überprüfung dieser neu entwickelten Hypothese eines der Arbeitsziele, als die deutschen Nord Victoria Land Expeditionen (Ganovex) dort 1979 ihre Arbeiten aufnahmen. An den bekannten zwei Granitgenerationen der Region wurden geologische, petrographische und geochemische Untersuchungen sowie Altersbestimmungen durchgeführt, deren Ergebnisse sich folgenderma\en zusammenfassen lassen.Die ältere, kambro-ordovizische Granitfolge steht, analog zur Situation in Australien, in enger Beziehung zu einer bedeutenden Orogenese, während sich zur jüngeren, devonisch-karbonischen Suite kein zugehöriges tektonisches Ereignis finden lie\. Dies steht im Gegensatz zur Situation in Australien/Tasmanien.Die S- und I-Typ Klassifikation, auf Nord Victoria Land angewendet, weist ähnliche Widersprüche auf, wie siePitcher (1982) zur Aufteilung der I-Typen in »kordillere« und »kaledonische« Sippen führten.Plattentektonische Modelle, die in den letzten Jahren für diese Region am mobilen Rand Gondwanas unabhängig von der Granitklassifikation nach geologischen und tektonischen Kriterien entwickelt wurden, erlauben es, die vonPitcher entwickelten tektonischen Bildungsmilieus für verschiedene Granit-Typen zu überprüfen:Die Charakteristiken der älteren (kambro-ordovizischen) Granite erlauben ein widerspruchsloses Einfügen in das aus anderen Kriterien abgeleitete Bild eines aktiven Kontinentalrandes über einer Subduktionszone.Für die jüngeren (devonisch-karbonischen) Granite dagegen, die im Charakter den »kaledonischen« I-TypenPitchers entsprechen, sind die für deren Bildung postulierten Vorgänge, nämlich Hebung und Dehnung nach einer Kollision, in Nord Victoria Land nicht erkennbar.Demnach erscheint zwar die KlassifikationPitchers sinnvoll, da sie in ihrer petrographisch-geochemischen Charakterisierung nachvollziehbar ist, aber das abgeleitete tektonische Milieu für die Bildung der »kaledonischen« Typen bedarf einer weiteren überprüfung.

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Résumé Dans le contexte du Gondwana, la Terre Victoria est le pendant antarctique de la zone plissée de Lachlan, en Australie Orientale, où la distinction entre granites S et I a été établie pour la première fois (Chappel &White 1974). C'est pourquoi la vérification de cette hypothèse a été portée au programme de l'expédition allemande à la Terre Victoria en 1979–80 (Ganovex).On connaissait à cette époque l'existence d'une génération cambro-ordovicienne et d'une génération dévono-carbonifère de granitoÏdes qui, par analogie avec l'Australie, avaient été rapportées à deux événements orogéniques différents. Nos investigations géologiques, pétrologiques, géochimiques et géochronologiques montrent que cette conclusion n'est vraie que pour les granites de la première génération. La seconde génération est, en fait, anorogénique. Il s'est avéré en mÊme temps que la répartition en types S et I ne correspond pas exactement aux observations de terrain. Par contre, la distinction introduite parPitcher (1982) parmi les granites I entre une série »de Cordillère« et une série »Calédonienne« peut expliquer les irrégularités que nous observons.Environ à cette époque, des modèles géodynamiques basés sur des considérations indépendantes de la classification des granites ont été proposés pour cette partie de la marge active du Gondwana. Ces modèles permettent de recouper les considérations sur l'environnement tectonique des granites, déduites de leur classification:Les caractères des granitoÏdes anciens, cambro-ordoviciens, s'accordent parfaitement au modèle d'une marge active surmontant une subduction.Par contre, pour les granitoÏdes jeunes, dévono-carbonifères, la situation tectonique postulée (soulèvement et fracturation post-collision) n'a pas pu Être confirmée sur la Terre Victoria.En conclusion, la classification dePitcher est applicable dans ses aspects pétrographiques et géochimiques, mais l'environnement tectonique qui préside à la formation de granitoÏdes de type »Calédonien I« n'est pas nécessairement le mÊme dans toutes les régions étudiées.

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- Lachlan, S I (Chappell & White, 1974). (GANOVEX) 1979 . , , . : - , , , , - , , - . S I , , (Pitcher, 1982) I . , , , , : — - — , . , - , , , , .. ., , - , , , , .

     

Geochemistry of metabasites from NE Sardinia, Italy: nature of the protoliths, magmatic trend, and geotectonic setting

Summary The metabasites of Montiggiu Nieddu occur as a lenticular body in the Hercynian migmatite complex of NE Sardinia and consist of two major lithological associations: ultramafic amphibolites and plagioclase-banded amphibolites, which are genetically related by processes of cumulate differentiation of an original tholeiitic magma. The ultramafic amphibolites consist of relics of igneous phases (anorthite, olivine, orthopyroxene, and clinopyroxene) and metamorphic minerals (orthopyroxene, clinopyroxene, plagioclase, garnet, chlorite, and amphibole) in variable proportions. Based on the distribution of the relics of igneous minerals three main compositional layers (A, B, C) have been identified in the ultramafic amphibolites. The plagioclase-banded amphibolites consist of dark-green and white bands made up of plagioclase, amphibole, garnet, and rare pyroxene in variable proportions. No relics of magmatic minerals were observed. The trace element patterns of the Montiggiu Nieddu metabasites are characterised by selective enrichment of incompatible elements of low ionic potential, such as Sr, Rb, Ba, and Th, and low abundance of K, Cr, Ni, and elements of high ionic potential (from Ta to Yb), which define a relatively flat trend similar to MORB composition. Ti, Y, and heavy rare earth elements are all positively correlated with Zr. This correlation suggests that no significant transport of these elements took place during metamorphism. The metabasites of Montiggiu Nieddu are characterised by low Ti, Ti/V, and Ti/Zr content, low rare earth and high-field strength element concentrations, and moderate selective enrichment in large-ion lithophile elements. They also show geochemical features similar to those of supra subduction zone tholeiites. The CaO-MgO diagram displays a segmented trend, which provides powerful evidence in favour of crystal-liquid separation during magmatic evolution. Received December 4, 2000; revised version accepted January 29, 2001     

The Precambrian geotectonic evolution of Africa: plate accretion versus plate destruction

The classical model of continental accretion and progressive cratonization, starting with an ancient nucleus onto which younger orogenic belts are welded (onion skin tectonics), has dominated geotectonic research for many years and has received new impetus with the general acceptance of the theory of plate tectonics. It has also been applied to the geotectonic evolution of large Precambrian crustal segments such as Africa.It is demonstrated, however, that new structural, geochronological and paleomagnetic data from Africa provide strong evidence for the existence of large cratonic continental plates since at least the Early Proterozoic which were later transected by linear mobile belts and thus partly destroyed. Crustal reworking and rejuvenation in these belts now gives the impression of younger orogens surrounding ancient “nuclei”.The geotectonic evolution of Africa is therefore characterized by plate destruction rather than by plate accretion with progressive cratonization, and only the “nuclei” have escaped this process.Many phenomena in the African mobile belts seem to indicate processes involving little or no relative motion of crustal plates or crustal shortening between them, and there is as yet no evidence of former oceanic plates to have been generated or consumed. It is therefore suggested that large-scale dispersive movements of major continental fragments were uncommon or absent in the Early and Middle Precambrian.Widespread drift may only have begun during the Late Precambrian/Early Paleozoic Pan African Tectogenesis, eventually leading to a crustal evolution as envisaged by the modern theory of global tectonics.     

Krakatau — a century of change

Krakatau — a century of change